This invention relates to an apparatus and process for measuring the work performed by a compressor.
Small compressors are widely used in the natural gas industry at production wells and storage facilities. Such compressors are used to increase the relatively low pressure of gas (1) emerging from natural gas wells, (2) leaving gas storage facilities or (3) being injected into storage wells, to the far higher pressures (usually of the order of Megapascals) which must be used in long-distance gas pipelines or for any other reason.
The compressor units used for this purpose conventionally contain a small gas engine, powered by natural gas bled from the supply being compressed, and a reciprocating compressor which performs the actual compression. The compressor units often operate unattended for protracted periods in remote locations and may run continuously or be started by timers, pressure switches or by remote control from a central control room. The gas consumption of the gas engines in such compressor units is substantial and it is desirable to determine periodically the efficiency at which such compressor units are operating in order to ensure that loss in efficiency of the compressor unit does not result in unnecessary consumption of the natural gas used as fuel.
To measure efficiency of the compressor unit, it is necessary to determine both the fuel consumption and the work performed by the compressor unit. Measurement of fuel consumption can readily be effected by conventional techniques known to those skilled in the art. However, hitherto no apparatus capable of measuring the work performed by the compressor unit and appropriate for long-term unattended use at remote locations, often without commercial power, such as those where many such compressor units are installed, have been available. Consequently, at present such compressor units are provided only with a revolution counter arranged to count the total number of engine revolutions of the compressor unit. Although such an engine revolution counter can in some cases give an indication of reduced efficiency of the compressor unit, in many cases an engine revolution counter may fail to detect loss of efficiency because the work performed by the compressor is not necessarily directly proportional to the engine revolutions. For example, if a compressor has bad valves, it can operate with a very low gas throughput, and reduction in gas throughput is not indicated by an engine revolution counter.
Accordingly, there is a need for an apparatus for measuring the work performed by a compressor, this apparatus being sufficiently small, economical and reliable to be suitable for installation on compressor sets used in natural gas production and storage facilities, and this invention provides such an apparatus.